Screening apparatus such as vibrating screen decks are used for a variety of applications and may comprise interchangeable square or rectangular screen elements that provide a screen surface upon which bulk material may be deposited and graded by size. Alternatively, the screen (commonly referred to as the screening media) may be of a cross-tensioned, length-tensioned or pre-tensioned media type having a sheet-like structure that extends between lengthwise extending sides of the screen deck. In particular, the tensioned screening media may be formed from wire mesh, metal sheet or reinforced polyurethane/rubber.
Wire mesh media is advantageous as it is easy to mount, relatively low cost and includes a large open structure to facilitate screening a greater range of stone or gravel fractions.
Cross-tensioned and length-tensioned screening media is mounted in the vibrating screen using hooks or fastenings attached to the side or end walls of the screen deck whilst pre-tensioned media is typically pressed downwardly onto the lower support frame by abutment brackets also mounted at the side or end walls. The screen media is supported from below by support beams spaced apart and arranged parallel to the sidewalls. The support beams are typically arranged at different heights in order to support media between the sidewalls in a crowned profile (or upwardly raised or hump-shaped) when secured in position.
Vibrating screen decks may also comprise modular screen elements in which the screening media comprises interchangeable panels that are tessellated together between the deck walls. An example modular screening deck is described in U.S. Pat. No. 4,219,412. Hybrid screen decks are also known comprising both the tensioned and modular media as described in US 2008/0257719. Modular screen decks are disadvantageous as the modular panels are manufacturer specific and are therefore higher cost and not as accessible as tensioned screening media.
Example tensioned screening media decks are described in JP 2012/076054 and WO 2005/092523. JP 2012/076054 discloses ‘cappings’ that are mounted on top of the parallel support beams to provide a cushioned support for the media and avoid accelerated wear due to friction. However, where the media comprises a continuously open structure along its length, it is common for stones or gravel to become lodged between the media and the cappings which both affects how the media sits upon the deck frame (by changing its orientation angle) and significantly increases the abrasion contact between the capping and the media to accelerate wear. It is therefore known to provide screening media with ‘blinds’ (elongate strip regions of the media that are devoid of screening apertures) spaced apart along the length of the media with these blinds configured to be supported directly from below by the cappings in an attempt to address the problem of stone entrapment. However, alignment of the ‘blinds’ with the cappings is not always optimised and also such non-standardised media tends to be higher cost and not as accessible. Accordingly, what is required is screening apparatus that addresses the above problems.